Many dispensers of liquid such as hands soaps, creams, honey, ketchup and mustard and other viscous fluids which dispense fluid from a nozzle leave a drop of liquid at the end of the outlet. This can be a problem that the liquid may harden, as creating an obstruction which reduces the area for fluid flow in future dispensing. The obstruction can result in future dispensing through a small area orifice resulting in spraying in various directions such as onto a wall or user to stain the wall or user or more disadvantageously into the eyes of a user.
Many dispensers of material such as creams and for example liquid honey have the problem of stringing in which an elongate string of fluid hangs from fluid in the outlet and dangles from the outlet after dispensing an allotment of fluid. With passage of time the string may form into a droplet and drop from the outlet giving the appearance that the dispenser is leaking.
Pump assemblies for fluid dispensers are well known. Such pump dispenser includes those invented by the inventor of this present application including those disclosed in U.S. Pat. No. 5,165,577, issued Nov. 24, 1992; U.S. Pat. No. 5,282,552, issued Feb. 1, 1994; U.S. Pat. No. 5,676,277, issued Oct. 14, 1997, U.S. Pat. No. 5,975,360, issued Nov. 2, 1999, and U.S. Pat. No. 7,267,251, issued Sep. 11, 2007, the disclosures of which are incorporated herein by reference. Of these U.S. Pat. No. 7,267,251 teaches a piston pump in which there is, in a charging stroke of a piston moving in a stepped chamber, drawback of fluid from an outlet through which the fluid is dispensed from the chamber in a dispensing stroke due to the provision of stepped chamber as having two portions of different diameter. Such an arrangement while advantageous has the disadvantage of requiring a stepped chamber.
Many previously known piston pumps suffer the disadvantage that the pistons for the pump are difficult to manufacture.